U.S. Pat. No. 4,038,187 is directed to improvements in microscreen drums and includes the specifications of a typical installation. In particular, the drum has a diameter of ten feet (3.104 meters). U.S. Pat. No. 4,123,362 is directed to an improved seal for such drum screen where flushing of the seal is required. The seal engages a machined surface of the drum track and prevents the unscreened water within the drum from escaping into the drum well containing the water which has passed through the screening of the drum.
All such seals must accommodate any eccentricity, out-of-roundness, misalignment and end play of the drum relative to its stationary parts. For practical reasons, all such seals should be readily installed after the drum is assembled and installed in the drum well and in particular, should be readily replaced without having to remove the drum from the drum well.
Typically, the upper one-fourth of the drum is above the flow to allow for backwashing of the screening. Accordingly, the circular element of the seal which is stationary may be discontinuous, provided only that its two ends extend above the maximum elevation of the flow. This element, of whatever form, is readily applied as shown in U.S. Pat. No. 4,123,362. That is, it is provided with a flat base which is held by a surrounding band against a circular rim projecting into the drum.
The search for a suitable rotating element has been more difficult. In the patent just mentioned, it is a machined, structural part of the drum track. Elements which are to be applied after the drum screen is installed must comprise segments of a circle, or comprise one or more lengths of material which may be curved and assembled to comprise a full circle.
The present invention provides an improved stationary element and utilizes a strip of material which is readily installed and forms a complete circular rotating element with virtually no gap between its abutting ends through which water may pass and with no projecting step which may cause some damage to one end of the stationary element.